Eliminating all sources of infection is extremely important when solutions of the aforementioned kind are prepared. Every stage in solution preparation must therefore be performed with the goal of eliminating the risk of contamination, thereby denying bacteria and other contaminants access to the solution being prepared.
Charging the syringe first with air is normally necessary when an injection syringe is to be filled with an injection agent. This is to expel air from the container from which the injection syringe is filled with injection agent to prevent the formation of any vacuum, which would impede filling, as the injection syringe fills. The air with which the syringe is charged is a potential source of contamination during preparation of an injection solution. Ordinary atmospheric air could contain different kinds of bacteria and other contaminants which might transfer to the injection solution and/or residual injection agent in the container unless special precautions are taken.
Injection syringes are therefore normally charged with air in special fume cupboards in which air is filtered before reaching the fume cupboard, thereby rendering the air aseptic, or air filling is performed in a sterile room. A relatively large investment is accordingly required at the liquid preparation site to ensure access to aseptic air. Many locations and situations have no access to fume cabinets or sterile rooms.
The provision of sterile air in a special container, from which air can be drawn for medication preparation, has therefore previously been proposed for the aseptic preparation of medication solutions.
Thus, U.S. Pat. No. 5,017,186 describes an apparatus comprising a container holding sterile compressed air and a vessel for use in the preparation of an injection drug. The use of means for connecting the container holding sterile air and the vessel makes it possible to transfer a charge of low-pressure sterile air from the container to the vessel. The vessel is equipped with means for sealing the container after the charge of sterile air has been received from the container. It also has walls, impermeable to air, and an opening which is sealed off with a punctionable, self-sealing membrane. According to U.S. Pat. No. 5,017,186, the walls of the vessel are essentially non-resilient and can be made of e.g. glass or acrylic plastic. The means for connecting the container holding sterile air and the vessel to be filled with sterile air consists of a coupling tailored to the kind of vessel to be filled, a pressure gauge and a valve. According to an alternative embodiment described in U.S. Pat. No. 5,017,186, a vessel containing sterile air and a bottle containing an injectable drug are provided in a tandem arrangement.
PCT/SE99/02144 describes a gas container for supplying aseptic air, the container having resilient walls.
Another example of aseptic air supplied in a container is provided in U.S. Pat. No. 5,102,406. The container is first charged with aseptic air which can be prepared at the fabrication site. When air is to be drawn into a syringe, the syringe needle penetrates a wall in the container and air is sucked into the syringe. The container is equipped with a wall filter through which filtered air can be replenished.
An injection syringe, equipped with a system of different filters for fluid filtration and a revolver-mounted connection channel for connecting the syringe cannula for fluid filtration, is also known from U.S. Pat. No. 4,820,276. The possibility of devising one of the filters as an air filter through which air can be drawn in is also cited as an option. As a result of its design, the syringe is rather complex and has interacting moving parts. Erroneous handling is also a risk since the connection channel could be connected to the wrong filter for a particular solution.